High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages

Abstract

Crystallographic observation of adsorbed gas molecules is a highly difficult task due to their rapid motion. Here, we report the in situ single-crystal and synchrotron powder X-ray observations of reversible CO 2 sorption processes in an apparently nonporous organic crystal under varying pressures at high temperatures. The host material is formed by hydrogen bond network between 1,3,5-tris-(4-carboxyphenyl)benzene (H 3 BTB) and N,N-dimethylformamide (DMF) and by π-π stacking between the H 3 BTB moieties. The material can be viewed as a well-ordered array of cages, which are tight packed with each other so that the cages are inaccessible from outside. Thus, the host is practically nonporous. Despite the absence of permanent pathways connecting the empty cages, they are permeable to CO 2 at high temperatures due to thermally activated molecular gating, and the weakly confined CO 2 molecules in the cages allow direct detection by in situ single-crystal X-ray diffraction at 323 K. Variable-temperature in situ synchrotron powder X-ray diffraction studies also show that the CO 2 sorption is reversible and driven by temperature increase. Solid-state magic angle spinning NMR defines the interactions of CO 2 with the organic framework and dynamic motion of CO 2 in cages. The reversible sorption is attributed to the dynamic motion of the DMF molecules combined with the axial motions/angular fluctuations of CO 2 (a series of transient opening/closing of compartments enabling CO 2 molecule passage), as revealed from NMR and simulations. This temperature-driven transient molecular gating can store gaseous molecules in ordered arrays toward unique collective properties and release them for ready use.in situ X-ray diffraction | nonporous organic crystalline material | CO 2 sorption G uest capture, storage, and removal in porous materials have been interesting topics in chemistry (1-7). The porosity of solids is one of the important factors determining their potential applications in guest storage. Because the storage generally uses void spaces interconnected through large open channels between the voids inside the crystal, nonporous or seemingly nonporous materials have received less attention. Over the past decades, nevertheless, due to the potential for selective guest capture and release in a controlled manner there have been attempts to study such materials which include calixarenes (8-17), 4-phenoxyphenol (18), biconcave molecules (19), tris(5-acetyl-3-thienyl)methane (20), metallocyclic complex (21), clarithromycin (22), and metalorganic frameworks (23, 24).Single-crystal X-ray diffraction can provide the crucial information on the binding interactions or structural changes of guest molecules within pores (25-27). However, the crystallographic observation of adsorbed gas adsorbents generally has not been possible due to the poor crystalline order of adsorbents upon removing residual solvent/guest molecules and the high mobility of gases even at low temperatures. Only a limited number of gas-adsorbed single-crystal struct...

Theoretical simulation of CO2 capture in organic cage impregnated with polyoxometalates

“…Additionally, we compared CO 2 adsorption and selectivity of nPOMs@SPC structures with other studies about organic cages. The highest adsorption amount of pure CO 2 in our structures is almost 4.0 mmolg −1 at 1 bar and 298 K, which is 3.9 mmolg −1 , 1.9 mmolg −1 and 3.8 mmolg −1 higher than the previous experimental findings in similar conditions . This is ascribed to the strong interaction between POMs and CO 2 .…”

“…The maximum selectivity of CO 2 over CH 4 in our materials is about 25 at 298 K and 15 bar in 6H 6 P 2 W 18 O 62 @SPC, which is inferior to 550 at 15 bar and 323 K in the research of Kwang et al and their value still upgrade with pressure . The highest S CO2/N2 in this study is about 26 at 1 bar, 298 K in 6H 6 P 2 W 18 O 62 @SPC, which is higher than the value of 18 at 1 bar, 323 K of Kwang's study . To further understand these high/low CO 2 adsorption and selectivity values, the reason will be discussed in the next.…”

Emission-Tunable Soft Porous Organic Crystal Based on Squaraine for Single-Crystal Analysis of Guest-Induced Gate-Opening Transformation

“…32−35 The difficulties lie in the lack of well-designed organic functional molecules and the extreme challenges in controlling the single crystallinity without severe fracturing during stimuli-responsive structural transformations. 19,36,37 Squaric acid architected by a highly symmetric fourmembered ring has been recently employed as an organic linker to construct porous frameworks. 38 The intrinsic oxygen atoms in the skeleton of squaric acid can act as natural functional sites for framework construction and selective molecular recognition through hydrogen bonds (H bonds) or Lewis acid/base interactions with special guest species, without the need for postsynthetic modification.…”

NO as a Reagent for Topochemical Framework Transformation and Controlled Nitric Oxide Release in Covalent Organic Frameworks

“…Using the post-NO CO2 adsorption isotherms as a reference, we calculated the initial heats of adsorption, Qst, adsorption capacities, and IAST selectivities over nitrogen for CO2 and NO (Table S1). For the selectivity calculations we chose a 15/85 gas mixture for CO2/N2 as commonly found in the literature, [41] and a 3/97 gas mixture for NO/N2, due to the low abundance of NO in exhaust gas mixtures. [42] We calculated the IAST selectivity of CO2 over nitrogen for TT-Imide-COF-NO and TTT-COF-NO as 9.22 and 6.44, respectively.…”